1. Field of the Invention
The present invention relates to a direct current (DC) brushless vibration motor and particularly to a DC brushless vibration motor comprising a stator formed by a singly-wound conductive wire as a single inductive coil and a rotary magnetic element eccentric to the rotation axis thereof to generate vibration.
2. Description of the Related Art
Motors with multiple coils wound by a single wire are widely known in the art. For instance, U.S. Pat. Nos. 6,700,275 and 6,850,019 adopt multiple coils wound by a single wire. The abutting coils have opposite winding directions. After the coils are energized with electricity, opposing polarization occurs. The coil structure consists of a single wire to form multiple coils and thus multiple magnetic poles will be present when coils are energized. During winding operation, after winding of a coil is finished, the winding machine has to be stopped, and the next winding rod is turned to the winding position to start the next winding action in the opposite direction. Such a process has to be repeated many times to cause the design of winding machines more complicated, the winding time longer, and the total cost higher.
These days miniaturized vibration motors have deeply permeated into people's life with the advent of digital era and aging of population. The most notable application is in the mobile phone. When a call is coming, there are generally two types of modes to alert users, one is the ring tone mode, and the other mute vibration mode. When a handset is set to vibration mode, a vibration motor must be used to generate vibration. The miniaturized vibration motor is also used in other digital mobile devices, entertaining game players, handheld game players and the like. In the industry of producing entertaining devices, the competition is fierce. To cater to fickle tastes of consumers, providing merely video and audio effects is no longer satisfied. Some manufacturers have provided consumers with touch stimulation. For instance, the Immersion Co. of U.S.A. has a number of patents that use touch technology on computer peripherals, such as a vibration mouse, vibration keyboard, vibration joy stick on game players, and the like. The vibration of those touch mechanisms can also be generated by the vibration motor.
On the evolution of the DC vibration motor, there were a bar-typed vibration motor and a flat-typed vibration motor in earlier days (such as U.S. Pat. No. 6,522,037). They all adopted contact brushes as means of commutation. Such a structure has a shorter life span, lower reliability, easily generates sparks and results in risky conditions. To remedy the aforesaid disadvantages, the brushless vibration motor has been developed. It adopts driver integrated circuit (IC) to sense the magnetic field of rotor as means of contactless commutation (such as U.S. Pat. Nos. 6,836,039 and 6,573,627).
Refer to FIG. 1 for the operation principle of a conventional double coils DC brushless vibration motor. As the DC brushless vibration motor adopts a contactless approach to commutate the current, the vibration motor usually includes a Hall IC, such as Melexis US79, which is a Hall IC to work with double coils. Each coil of the motor has two ends, and one end of each coil connected to an O1 end and an O2 end of the IC, respectively. The other end of each coil is grounded. When the Hall IC senses a magnetic north pole of the magnet, O1 is set to a higher potential than ground and current will start to flow, from O1 through the coil at the right side, to the ground. Assumed the coil at the right side is wound in clockwise direction, as the magnetic north pole of the magnet is sensed by the Hall IC on the upper side, and the current flows from O1 to the ground. Because the coil is wound in clockwise direction, the coil generates a magnetic south pole according to Ampere's rule (right-hand rule), to repulse the magnetic south pole of the magnet. As a result, rotation is generated. Meanwhile, O2 end is open, the coil at the left side is not conductive and no magnetic field is generated. The motion is solely driven by the mutual repulsion between the magnetic field generated by the coil at the right side and the magnet. When the Hall IC senses the magnetic south pole of the magnet, O2 is set to a higher potential than ground, thus the current flows from O2 through the coil at the left side to the ground. By means of energizing the two coils alternately to generate a magnetic force repulsive to the facing magnetic poles of the magnet, a continuous rotation of the magnet can be maintained. However, such a design always has a coil on one side in an open and non-conductive condition. The rotor is driven by the electromagnetic force generated by only one energized coil, and the other un-energized coil makes no contribution to the driving force of the rotor. Moreover, the structure of the DC brushless vibration motor in aforesaid embodiment employs at least two coils, increasing the number and cost of motor parts. Fabrication difficulty and cost are also higher.
In terms of means of vibration generation, U.S. Pat. No. 6,836,039 discloses a technique that includes an annular magnet with six planar poles. A weight object is added to one side so that the rotor has a gravity center eccentric to its rotation center to generate vibration. Such a design increases the load of the rotor. More input electric energy is needed. Moreover, adding the weight object makes the profile of the motor higher, so it is difficult to miniaturize the motor. U.S. Pat. No. 6,573,627 discloses a technique that includes an annular magnet with four planar poles located eccentrically on a rotor disk. When the rotor disk rotates, the eccentric gravity center of the rotor causes vibration. However, due to space constraint, the eccentricity between the annular magnet and the rotation center is limited. As a result, the vibration intensity cannot be increased as desired. To sum up, the aforesaid DC brushless vibration motors have many drawbacks, such as complicated structures and complicated winding of the induction coils, difficult fabrication, and higher profiles, which cannot be shrunk and miniaturized as desired.